Current blow-molding machinery is designed to manufacture hollow plastic containers by extruding a parison between opposed, parted mold halves. The mold is then closed and air is injected into the parison, blowing and distending it outward so that it conforms itself to the inner contours of the mold which match the outer shape of the bottle to be produced. The newly formed container is allowed to harden, then is extracted or dropped from the mold.
Some plastic bottle manufacturers produce blow-molded articles by using rotary blow-molding machines. A typical rotary blow-molding machine includes a rotating carrousel that carries two or more mold stations around a circular mold station path. Each mold station includes a mold with a mold cavity. The carrousel is indexed to hold each mold station momentarily motionless at each of a series of blow molding "workstations". As used in the specification and claims, a "workstation" is defined as a position where each mold station must pause in its circular path for a particular operation to be carried out. A "workstation series" is defined as a progression of workstations necessary to complete a blow molding process on a single mold station in a single carrousel revolution. Blow molding operations are carried out sequentially on each mold as each mold station rotates through a workstation series, pausing momentarily at each workstation in the series.
Rotary blow-molding machines may, of course, include any number of molds and workstations, and may include more than one workstation series arranged around a single mold station path. In rotary blow-molding machines with a single workstation series, there is a simple relationship that determines the minimum number of carrousel indexing positions: The carrousel must pause in a number of indexing positions that is at least equal to the number of workstations in the series and at least equal to the number of mold stations. The reason for this is that each mold station must pause at each workstation in the series one time during each carrousel rotation to complete the blow molding process at each mold station. As long as the number of mold stations is equal to or greater than the number of blow-molding workstations where each mold station must pause, then the carrousel must index at least as many times as there are mold stations. If, for example, there are only two mold stations spaced 180 degrees apart, and only one workstation where each mold station must pause, the carrousel must index 180 degrees twice during each rotation to make each mold station stop at the workstation one time.
In many rotary blow molding machines the only blow-molding operations that require a mold station to pause at a fixed workstation are the parison-extrusion and article-release operations. However, following the extrusion station and preceding the release station the process requires that there be sufficient "blow time" and cooling time for each blow-molded article to properly form and harden in the cavity within each mold.
To provide sufficient "blow time" and cooling time, designers usually position the release station to immediately precede the extrusion station. With the release station positioned in this way, each mold and mold station must travel a large angular distance around the mold station path from the extrusion station to the release station, and a smaller angular distance from the release station back to the extrusion station. The average carrousel angular velocity must be slow enough to allow each mold sufficient "blow time" and cooling time as it travels this angular distance.
By adding more mold stations and indexing pauses to a carrousel, designers are able to minimize the impact that these cooling and "blow time" requirements have on the total average time it takes to produce a blow-molded bottle. While cooling and blow-time requirements must generally remain the same, additional mold stations and indexing pauses allow more extrusion and release operations to occur per revolution. However, carrousel space limitations and the absence of a workstation in the typically small angular distance between the release station and the extrusion station make it difficult to add another operation, such as in-mold labeling, to the blow-molding process.
Current rotary blow-mold carrousels are generally designed to index a number of times equal to the number of mold stations supported on the carrousel. For example, U.S. Pat. Nos. 3,854,855, 3,936,521 and 3,941,863 to Pollock et al., each disclose six-mold-station carrousels that index six times per revolution; U.S. Pat. No. 4,439,127 to Frohn discloses a five-mold-station carrousel that indexes five times per revolution; and U.S. Pat. No. 4,233,019 to Sawa et al., U.S. Pat. No. 4,834,643 to Klinedinst et al. and Japanese Pat. No. 402,165,922A to Calsonic et al. each discloses four-mold-station carrousels that index four times per revolution.
The reason that engineers design rotary blowmolder carrousels to index a number of times equal to the number of mold stations is because the carrousel must index at least this number of times to cause each mold station to pause at each workstation. However, as designers increase the number of mold stations in a rotary blow-molder, they must either enlarge the carrousels to accommodate the larger number of mold stations, or must make the mold stations smaller--so that more can fit on the same size carrousel.
Moreover, for designers to add additional operations such as in-mold labeling to rotary blow molding machines with, as is found in the prior art, the same number of indexing positions as mold stations, they must displace the article take-out workstation with the new in-mold labeling apparatus. This requires that the take-out workstation be re-located to the next preceding workstation along the mold station path. This, in turn, compresses all other blow molding operations, including cooling and blowing, into a smaller portion of the mold station path. This compression would require the carrousel to either be larger or to rotate more slowly to allow sufficient cooling and blow time. It would also constitute an inefficient use of the latter portion of the mold station path between the relocated take-out station and the extrusion station.
When in-mold labelers (IMLs) have been incorporated into rotary blow-molding machines, the IMLs have been adapted to position labels on inner mold cavity surfaces of non-indexing-type blow-molding machines. Consequently, the labels must be applied "on-the-fly", i.e., as the mold cavities move continuously around a circular path. Some current systems have accomplished this by incorporating structures that cancel relative motion between each label and its target mold cavity by accelerating the labels to match the radial velocity of their target cavities before applying the labels. Other such systems employ stationary IMLs with "picker heads" that retrieve labels from label magazines and deposit the labels into moving mold cavities. Some of these systems are capable of servicing more than one mold cavity at a time by employing multiple label magazines and label pickers. In such systems the label pickers, on each pass, transfer labels from all the magazines to all the cavities.
For example, U.S. Pat. No. 4,582,474 to Ziegler (the Ziegler patent) discloses a non-indexing rotary blow-molding machine with multiple molds and an IML with multiple carriage-mounted label pickers that move labels from multiple pairs of label magazines and deposit them into cavities in opposing halves of multiple molds. The Ziegler patent does not disclose means for properly aligning the labels with the mold cavities without adjusting the orientation and/or motion of the label pickers.
U.S. Pat. No. 4,824,630 to Mohney (the Mohney patent) discloses a non-indexing rotary blow molder with multiple mold cavities and an IML with multiple carriage-mounted label pickers for moving labels from a web of label material and depositing them into cavities in the opposing halves of multiple molds.
U.S. Pat. Nos. 4,585,408 and 4,721,451 to Darr disclose in-mold label dispensers for blow molding machines. The label dispensers disclosed in these patents include label magazines that are linearly adjustable in three dimensions, both collectively and individually. The Darr '408 patent also discloses label carriers mounted on plastic components to prevent mold damage. The plastic components prevent mold damage by breaking if a mold is closed with the label carriers inserted.
R&B Machine Tool has manufactured an IML for servicing a single-indexed rotary blow-molder. A single-indexed rotary blowmolder includes a carrousel indexer that pauses a carrousel in a number of indexing positions equal to the number of mold stations. Rather than attempting to accurately position a label on a moving cavity surface, this R&B system applies labels during "dwell" periods when the rotational motion of the rotary carrousel is momentarily halted. However, this R&B system (R&B single-cavity IML) services only one mold cavity at a time. In other words, the R&B single-cavity IML is designed to apply labels to opposite halves of a single cavity in each mold during each carrousel cycle. The R&B single-cavity IML includes a single pair of label magazines and a single pair of suction cup groupings (picker heads) for picking labels out of the magazines and carrying them to an open mold cavity halves. Because the R&B single-cavity IML services only a single mold cavity at a time, the production rate of a rotary blow-molder using this IML system is limited.
What is needed is a combined rotary blow-molding machine and IML that accurately labels blow-molded articles while producing larger numbers of such articles per carrousel rotation.